16 But I tremble to say it; the audacity staggers me. I hear, And the Word was God; I, whom the prophets have taught that God is One. To save me from further fears, give me, friend Fisherman, a fuller imparting of this great mystery. Show that these assertions are consistent with the unity of God; that there is no blasphemy in them, no explaining away, no denial of eternity. He continues, He was in the beginning with God. This He was in the beginning removes the limit of time; the word God shows that He is more than a voice; that He is with God proves that He neither encroaches nor is encroached upon, for His identity is not swallowed up in that of Another, and He is clearly stated to be present with the One Unbegotten God as God, His One and Only-begotten Son.
Source: On the Trinity (New Advent)